1. Technical Field
The present invention relates to a linear vibration motor.
2. Description of the Related Art
Generally, a vibration motor, which is a component converting electrical energy into mechanical vibration using a principle of generating electromagnetic force, is mounted in a mobile communication terminal, a portable terminal, and the like, to be used for silently notifying a user of call reception.
Further, in a situation in which small-sized and high quality components are required in a mobile communication terminal in accordance with the trend in which a multi-functional mobile communication terminal has been prominent due to the rapid expansion in wireless communication and mobile phone markets, performance and a technology of a vibration motor has also been developed daily in order to overcome a disadvantage of an existing product and significantly improve quality.
In addition, as the release of a cellular phone having a large-sized liquid crystal display (LCD) screen has rapidly increased in recent years, a touch screen scheme has been used. As a result, the linear vibration device has been used to generate vibration at the time of touch, such that the demand thereof has increased.
Meanwhile, performance particularly required in the vibration according to the touch of the touch screen is as follows. First, as the number of vibration generations according to the touch becomes larger than that of vibration generations at the time of call reception, an operating lifespan needs to increase. Second, in order to allow users to feel the vibration at the time of touch, a response speed of the vibration needs to increase in accordance with a touch speed of the screen.
The linear vibration motor mainly used according to the prior art has used a scheme of generating rotational force to rotate a rotor part having unbalanced mass, thereby obtaining mechanical vibration and generates the rotational force by supplying current to a rotor coil through a rectifying action by contact between a brush and a commutator.
However, in a brush type structure using the commutator as described above, at the time of rotation of the motor, the brush causes mechanical friction and electrical spark while passing through a gap between the commutator and a segment to lead to abrasion and foreign materials such as black powders, or the like, thereby reducing a lifespan of the motor.
In addition, a time is required to arrive at a target vibration amount due to rotation inertia at the time of application of voltage to the vibration motor, such that it is difficult to implement vibration appropriate for a touch screen phone.
A linear vibration motor, which is a vibration motor capable of satisfying the above-mentioned characteristics, has a resonant frequency determined by a spring and a vibrator part connected to the spring and is oscillated by electromagnetic force to thereby generate vibration. In addition, the electromagnetic force is generated by the interaction between a magnet of the vibrator part and current applied to a coil of a stator part and having a predetermined frequency.
Further, the vibrator part of the linear vibration motor does not use a rotation principle of the motor but is oscillated by electromagnetic force having a resonant frequency determined using a spring, which is an elastic member installed in the vibrator part and a weight body hung on the spring to thereby generate vibration.
As a result, the spring connects a case or a bracket, which is the stator part, and the weight body, which is the vibrator part, to each other and determines the resonant frequency together with the weight of the weight body.
However, the spring includes frequencies that are multiple components other than the resonant frequency, and the spring repeatedly extended and compressed also generates frequencies that are not the multiple components at the time of being touched to the weight body. Therefore, the frequencies that are the multiple components and the frequencies that are not the multiple components have an effect on the resonant frequency, such that a desired vibration displacement may not be obtained and noise may be caused. In accordance with sliminess and lightness, as a design margin of the spring becomes short, the noise increases.
FIG. 8 is a graph showing a touch amount according to a frequency of a linear vibration motor according to the prior art. It could be appreciated that in the linear vibration motor in which a connection piece between an inner ring and an outer ring includes four elastic members, a peak (part P) by a touch of the elastic member occurs at a frequency between 5 to 6 kHz.
As a result, the linear vibration motor according to the prior art is repeatedly extended and compressed at the time of linear vibration, such that a touch sound occurs between the linear vibration motor and a stator part or a vibration part connected to the linear vibration motor.